About 1.2 million Americans are HIV positive and another 50,000 are infected each year, according to the Centers for Disease Control and Prevention (CDC).

Medications that suppress – but don’t cure – the disease have been available for several years. But a preventive medication has eluded researchers… until now.

The Food and Drug Administration (FDA) recently announced that an existing HIV combination oral medication, Travuda, which is already approved and widely used for of HIV infection treatment, may also prevent the disease in the first place if taken every day.

A study published in the New England Journal of Medicine in 2010 reported that a once-a-day dose of Travuda reduced the incidence of HIV infection by up to 44% in men who have sex with other men. Other high-risk groups who may also benefit include gay men with multiple partners who do not use condoms consistently, people in relationships with someone who is HIV positive and prostitutes.

As promising as this breakthrough is, a number of experts have serious concerns about HIV strains becoming Travuda drug-resistant. Here’s why:

Preventing HIV transmission with Travuda is dependent on two factors: The drug would have to be 100% effective and patients would need to be 100% compliant in taking the daily dose. Anything less could lead to increased drug resistance, and even the FDA acknowledges that resistance is likely to occur among people who become HIV positive while taking the drug preventively.

Unfortunately, Travuda is not 100% effective, and in one study, only 10% of patients took the drug as instructed. Although the drug is generally well tolerated, it can cause stomach upset in the first weeks it is taken. Patients must also be monitored for kidney problems and bone thinning.

Another hindrance toward 100% compliance is Travuda’s high price, more than $1,000 per month. Stanford University researchers have estimated the 20-year cost of preventive administration of Travuda to all gay and bisexual men at nearly $500 billion.

If Travuda gains widespread preventive use, strategies will be needed to minimize the emergence of resistant strains. The Stanford team suggests that targeting men with five or more sexual partners a year for therapy could be far more effective. They estimate that 41,000 new infections could be prevented over the next 20 years, at a cost of $16 billion if just 20% of these high-risk individuals were treated.

Careful monitoring of patients on Travuda to ensure daily compliance and HIV status is recommended. Patients who turn HIV positive while on Travuda therapy would quickly discontinue treatment in an effort to lesson the likelihood of resistance.

The bottom line? Along with this promising breakthrough in preventive HIV care, there are also significant concerns about compliance, cost and emergence of resistant strains.

The FDA has yet to issue a final ruling on clearance of Travuda for preventive use, but physicians are already prescribing the drug for such use off-label. In the meantime, we’ll have to rely on current HIV preventive measures, including: